A commonly occurring complication associated with leakage of colonic bacteria into the peritoneum is intraabdominal sepsis and abscess formation. An abscess is an encapsulated collection of bacteria, lymphocytes, macrophages, polymorphonuclear leukocytes and fibrin that forms in response to bacterial insult or contamination within a tissue or body cavity, such as occurs during a surgical procedure, trauma or diseases such as appendicitis or cancer. Invasion of the exposed body area by the bacteria may occur in a localized area within the peritoneal cavity, retroperitoneal space, pelvis or other spaces or organs in the body. The infected tissue area remains relatively immune to antibiotics which are unable to penetrate the tissue structures and effectively clear walled-off bacteria. If the abscess is left untreated, it may cause fever, prolonged hospitalization, and in some cases mortality. If the abscess ruptures, it will release its bacterial contents into the peritoneal cavity, which can in turn lead to recurring sepsis in these patients. Currently when abdominal surgeries are performed, antibiotics are administered prophylactically as well as postoperatively. However, once an abscess has formed, the major course of action is further surgical intervention to drain the offending abscess, a time-consuming and costly procedure.
It has been impractical to immunize patients against abscess formation such as in the case of intraabdominal surgery because there simply are too many strains of bacteria capable of causing abscess formation, and protection against one would not confer protection against another. It furthermore is unsettled whether vaccination and consequent induction of an immune response would confer adequate protection against abscess formation by any particular bacterium. There also exist problems and dangers associated with administering live or attenuated strains of bacteria to humans, further discouraging efforts to produce vaccines containing a large number of different bacteria.
Capsular polysaccharides of bacteria can be found covering the surface of some bacteria pathogenic to humans. Polysaccharides have been characterized as T cell-independent antigens that elicit only humoral antibody responses. Although many polysaccharides have been shown to be immunogenic, some are only weakly immunogenic at best.
Bacteroides fragilis is a predominant obligate anaerobe isolated from intraabdominal abscesses. The capsular polysaccharide complex (CPC) has been identified as the region of B. fragilis which causes abscess formation. This carbohydrate complex covers the surface of B. fragilis. The isolated complex alone can interact with the host immune system, in the presence of adjuvant (sterile cecal contents and barium sulphate), to elicit a patho-biologic response that results in fully formed intraperitoneal abscesses in individuals injected intraperitoneally with the complex. Studies were performed in rodent models in which B. fragilis or its CPC were injected intra peritoneally. Both intact B. fragilis and CPC alone provoked abscess formation associated with intraabdominal sepsis.
It was investigated whether the CPC of B. fragilis could be used to immunize subjects against subsequent infection and abscess formation by B. fragilis. It was by no means predictable that this would be possible based upon the property of CPC alone to provoke abscess formation since “immunity” and abscess formation are not known to result from remotely related immunological responses. When CPC was administered subcutaneously it was found to confer immunological protection against intraperitoneal CPC-mediated abscess induction in a rat model. Protection against abscess formation by this polysaccharide complex was determined to be mediated by a T cell-dependent host response.
Although subcutaneous administration of either B. fragilis or CPC is sufficient to protect animals against abscess formation subsequent to challenge with B. fragilis or CPC, neither conferred immunity against other bacterial strains, as was expected. They therefore have no use as a “vaccine” for abscess formation caused by the multitude of organisms normally found in the colon.
The CPC consists of two distinct high molecular weight polysaccharides, termed A and B. Each polysaccharide is composed of distinct oligosaccharide repeating units possessing uncommon constituent sugars with free amino, carboxyl and phosphonate groups. Polysaccharide A (PS A) has a tetrasaccharide repeating unit with a balanced positively charged amino group and negatively charged carboxyl group. Polysaccharide B has a hexasaccharide repeating unit, including an unusual 2-amino ethylphosphonate substituent containing a free amino group and negatively charged phosphate group. The galacturonic acid residue contains an additional negatively charged carboxyl group. Ionic interaction between the two saccharide chains tightly links polysaccharides A and B into the high molecular weight CPC complex. The complex capsular motif is a conserved trait for all strains of B. fragilis that have thus far been examined.
Recently it was discovered that polysaccharides having a particular structural motif can protect animals against challenge with abscess-inducing bacteria. U.S. Pat. Nos. 5,700,787 and 5,679,654. Preferably the polysaccharides are polymers of repeating units of a charge motif characteristic of polysaccharide A of B. fragilis, the motif being a positively charged free amino moiety and a negatively charged moiety selected from the group consisting of carboxyl, phosphate, phosphonate, sulfate and sulfonate. Such polymers are capable of inducing “cross-protection.” That is, a single polymer can produce protection against abscess formation by a variety of bacteria. Thus the polymers are useful for inducing protection against abscess formation associated with surgery, trauma or diseases that predispose the host to abscess formation. A pharmaceutical preparation of the polymer is administered to a subject in conjunction with intraabdominal surgery or upon presentation of a predisposing condition.
It was also reported in the prior art that while several types of cytokines, such as interleukin-10 (IL-10), are useful as general immunomodulators for blocking abscess formation, other cytokines, such as interleukin-2 (IL-2), tumor necrosis factor, and interferon, may participate in abscess formation, since antibodies specific for such substances can help block abscess formation. U.S. Pat. No. 5,700,787.
Postoperative surgical adhesions are a major complication of abdominal, pelvic, gynecologic, cardiothoracic, orthopedic and neurosurgical surgeries. Surgical adhesions within the abdomen are associated with a high morbidity rate and can be fatal. They can result in bowel obstruction and organ failure. There are approximately 1.5 million abdominal surgeries performed every year in the United States alone. Of these surgeries 25 to 35 percent of cases result in the development of surgical adhesions. Repair of adhesions that cause bowel obstruction and organ failure require reoperation for their removal.
Traditionally these adhesions have been thought to be caused by a combination of factors including manipulative trauma and drying of the tissues during the surgery itself. A number of techniques attempting to ameliorate these problems have been previously described. Current clinical methods directed toward reducing the formation of postoperative surgical adhesions generally rely on placement of a film or gel directly into the operative site with the intention of creating a physical barrier between surfaces likely to become involved in adhesion formation. These methods remain cumbersome for the surgeon. Highly concentrated solutions of a number of polymers have been used to coat the surgical area before and during surgery so as to minimize the drying and act as cushion to prevent some of the manipulative trauma. Examples of the techniques are described in U.S. Pat. No. 4,819,617 to Goldberg et al. and U.S. Pat. No. 4,886,787 to De Belder et al. Among the materials used are polyvinylpyrrolidone (PVP), dextrans, carboxymethylcelluloses, and a number of other polymers such as protein or polypeptide solutions.
One polymer which has been used to reduce postoperative surgical adhesion formation is hyaluronic acid (HA). A series of patents by Goldberg et al., particularly U.S. Pat. No. 5,140,016, shows the use of pretreatment of surgical sites with hyaluronic acid solutions as a means of preventing surgical adhesions. Goldberg disclosed that dilute solutions of high molecular weight HA (>500 kDa) are effective at concentrations of 0.01 to 0.6% (weight/volume) when used for surgical adhesion prevention. A 0.01% solution of about 1500 kDa molecular weight HA effectively prevents all severe intra-abdominal adhesions in a rat adhesion model that normally produces more than 70% adhesions.
Like abscess formation, postoperative surgical adhesion formation involves fibrin deposition within a site of inflammation. While the exact mechanism underlying adhesion formation remains unknown, much attention has been directed to the apparent role of transforming growth factor beta (TGF-β), particularly TGF-β1. TGF-β is a key factor in the regulation of the inflammatory response and the production of extracellular matrix by fibroblasts. These two processes are linked in the formation of fibrous adhesions following abdominal surgery. TGF-β also increases the synthesis of integrin receptors, thereby enhancing interaction between cell and extracellular matrix. Using a model of abdominal adhesions in rats, Lucas et al. demonstrated that rats injected with anti-TGF-β1 had significantly lower adhesion scores than rats receiving control IgG, anti-TGF-β2 or panspecific anti-TGF-β. Lucas, P A et al. J Surg Res 65:135 (1996).
U.S. Pat. No. 5,679,658 to Elson discloses a method of preventing surgical adhesions in which a surgical site is coated with an effective amount of a covalently crosslinked N,O-carboxymethylchitosan (NOCC) gel and lavaged with a solution of uncrosslinked NOCC after surgical manipulation. NOCC is a polymer in which carboxymethyl substituents are present on some of both the amino and primary hydroxyl sites of the glucosamine units of the chitosan structure. U.S. Pat. No. 4,619,995 to Hayes. NOCC can be crosslinked into a stable gel using conventional methods known in the art. Krause et al. investigated the possibility that effects of NOCC on adhesion formation reflect the modulation of TGF-β activity. Krause, T J et al. J Invest Surg 11:105 (1998). Using a cecal abrasion model in the rat, Krause et al. reported that NOCC suppresses the levels of an inhibitor of cell proliferation released into serum and peritoneal cavity. However, this activity is distinct from known forms of TGF-β as determined using both TGF-β neutralizing anti-sera and a TGF-β resistant cell proliferation assay. Krause et al. concluded that at least one potential effect of NOCC involves a mechanism distinct from TGF-β inhibition.
In view of the foregoing, a need still exists to develop compositions and methods for treating and/or preventing abscess formation, surgical adhesion formation, and other immune-related disorders.